This invention relates to an apparatus for cutting cord reinforced rubber sheet and more particularly an apparatus for longitudinally cutting such cord reinforced rubber sheet into strips of ply stock of the type employed in the construction of pneumatic tires.
In pneumatic tires, certain of the principal components thereof are sheets or plies of cord-reinforced rubber which form the carcass and belts of the tires. In the manufacture of such plies, parallel reinforcing cords of fabric, glass, or metal are pressed through a pair of rolls in cooperation with calendering rolls which work unvulcanized rubber onto the parallel cords as they pass through the rolls to form a continuous rubber sheet with reinforcing cords embedded therein. Thereafter, the sheet is cut diagonally or "bias" cut into strips so that the parallel cords are disposed at a desired "bias" angle to the cut edges. This bias cutting operation, as well as a bias cutter therefor, are described, for example, in U.S. Pat. No. 4,069,729.
The bias cut strips are then spliced end to end to form the reinforced rubber sheet with the cords therein located at a desired "bias" angle relative to the longitudinal center line of the sheet. The strips which form this sheet are sometimes bias cut to a width which is greater than a particular tire ply specification width so that the sheet formed from the strips can supply more than a single width of tire ply stock. For example, the sheet of spliced bias cut strips from which belt ply stock of a particular width is taken may be formed to twice that particular width. In this instance, the bias sheet formed from strips from the bias cutter must then be longitudinally cut into predetermined widths of ply stock before being usable in the construction of a tire.
An apparatus cut to a multiwidth sheet normally includes a slitting device comprising a lower stationary anvil-type blade member and an upper rotating disc-like slitter cooperating in shear with the anvil-type blade. The anvil-type blade member usually has a linear or straight cutting edge.
An anvil-type blade cooperates with a rotating disc-like slitter to shear the sheet that is fed to and from such slitting device. The rotation of the peripheral cutting edge or edges on the rotating slitter induces a downward shearing action to interact with the linear cutting edge of the anvil-type blade member.
The sheet which is longitudinally cut to form the strips sometimes can have an irregular edge. In these instances, the longitudinal slitting device may be augmented by a trimmer to maintain the sheet at a uniform width by trimming the irregular edge of the sheet.
A trimming device is usually located beside the slitting device and usually comprises a lower stationary anvil-type blade member and an upper rotating disc-like trimmer similar to the slitting device.
The interaction of the rotating disc-like slitter or trimmer with a stationary anvil-type blade wears the linear cutting edge of the anvil-type blade rapidly. This requires frequent blade changes resulting in downtime of the apparatus, necessary maintenance to replace or sharpen the worn blades and misalignment between the blade and the rotating slitter or trimmer.
Use of a linear edge anvil blade which reciprocates, such as described in U.S. Pat. No. 3,858,474 can prolong somewhat the periods of use of the anvil blade before sharpening or replacement is necessary. However, the changing of the blade can still result in misalignment of the reciprocating anvil cutter and the rotating slitter.
Another way to prolong lower anvil life which has been suggested is to replace the linear anvil cutter with an indexing or slowly turning disc-like blade with a plurality of linear edges along its peripery. This disc-like lower blade requires an additional means to turn the cutter at the desired slow speed and can result in slitting operations which are not as precise or "clean" as when lower stationary anvil-type blades are used.